Patent applications WO2011/054553 and WO2011/054845 (both in the name of GlaxoSmithKline LLC) disclose the compound 2-[(4S)-6-(4-chlorophenyl)-1-methyl-8-(methyloxy)-4H-[1,2,4]triazolo[4,3-a][1,4]benzodiazepin-4-yl]-N-ethylacetamide as a BET family bromodomain inhibitor and describes therapeutic uses thereof. The chemical structure of this compound is represented by formula (I):

There remains the need to identify a form of the compound of formula (I), which provides suitable properties for its development as a pharmaceutical product. In particular, a form of the compound of formula (I) which provides one or more suitable properties such as hydroscopicity, stability, solubility and processability is required.